1. Field of the Invention
The present invention relates to a method for bleaching a long cloth continuously, with particular in tension to give an excellent result in saving energy, and an apparatus therefor.
2. Description of the Related Art
In a conventional method for bleaching a long cloth produced industrially with the use of sodium chlorite, an aqueous bleaching solution comprising sodium chlorite together with an organic acid such as formic acid and acetic acid or an inorganic acid such as phosphoric acid and sulfuric acid, is applied to a cloth to be bleached at tile ordinary temperature, and the resultant cloth is subjected to wet heat treatment in a treating chamber in gaseous or liquid medium for carrying out the bleaching treatment in object continuously.
To describe said method for bleaching a long cloth continuously for practical use in detail, the pH of the aqueous treating solution is controlled to 3-4, and after the cloth is soaked with said bleaching solution at the ordinary temperature by transporting the cloth continuously therethrough, the cloth is squeezed by using a squeeze roll in order to render its solution content appropriate (about 100%), and then the resultant cloth is transported through a bleaching chamber in gaseous or liquid medium continuously. In the bleaching chamber, the cloth is folded to form piles in succession, and subjected to the bleaching at a temperature in the range of 80.degree.-90.degree. C. for about 40-60 minutes. After a sufficient treating time, the piles of the thus treated cloth are taken out of the chamber in succession, and thus the continuous bleaching of a long cloth is ended.
However, in such an instance, since the cloth is piled in succession in this way, the temperature distribution of the interior and the outside of the cloth thus piled is not uniform, and the temperature of the interior of the pile is unavoidably low. Accordingly, the reaction velocity, i.e., the bleaching speed, is low at the interior of the piles. This is the reason why it needs a long time of about 40-60 minutes as above mentioned in order to complete the bleaching up to the interior of the piles sufficiently. Moreover, since the treating degree differs place after place, uniformly bleached product can hardly be obtained, and further, since the treating time is unavoidably long as above mentioned, it is unavoidable that creases are formed in the cloth due to folding, particularly at the bottom part of the piles owing to the weight of the cloth itself. The formation of creases is especially remarkable in a high density cloth and the one with a fine yarn number.
Separately, to avoid the defect of forming piles of cloth, in bleaching a long cloth continuously, a method has been proposed to transport a cloth to be bleached continuously through a wet heat treating chamber with no tension continuously by using a plurality of guide rolls or a piler. However, since it needs a long treating time of about 40-60 minutes thereby for the bleaching of each part of a long cloth uniformly, the length of the cloth staying in a chamber becomes unavoidably very long, and accordingly the number of guide rolls necessary for transporting the cloth continuously becomes very numerous and the size of the piler becomes very large. In calculating, for trial, the length of a cloth necessary to stay in the wet heat treating chamber under the condition that the passing speed of a cloth therethrough is 100 m/min as usual in the similar treatment in a wet heat treating chamber, the length of the cloth staying in the treating chamber becomes unavoidably very long as 4,000-6,000 meters when the bleaching time is so long as 40-60 minutes as in the above-mentioned case. Therefore, it is obvious that such a proposal is by no means practical.